1. Field
Embodiments of the present invention generally relate to inflatable modules.
2. Background Art
Inflatable modules are well known in the art, as disclosed in U.S. Pat. No. 6,547,189 (hereinafter “Raboin”) assigned to the assignee of the present invention, which is hereby incorporated by reference in its entirety. Typically, an inflatable module is lightweight, collapsible, and compact prior to deployment, and is capable of being subsequently inflated to provide relatively large volume for storage, containment, human habitation, shelter, or work, as well as for space flight.
FIG. 1 shows a typical inflatable module 10, which may withhold a relatively high pressure of an internal fluid, such as air or other gas or liquid, and may be made to any desired shape and size. The inflatable module 10 is shown in its inflated configuration and includes a rigid core 12 and an inflatable shell. The inflatable module 10 may also include a structural pass-through 14 (hereinafter “rigid member”) disposed in the inflatable shell, such as a window, fluid port, hatch, connecting tunnel, etc. In the embodiment shown, the rigid member 14 is shown as a window.
The inflatable shell has two primary components: a restraint layer and a bladder. The restraint layer is the primary load bearing layer of the inflatable module 10 and reacts as a membrane to the entire pressure load. The restraint layer is typically fabricated from various high strength flexible materials. FIG. 2 shows a portion of the restraint layer 20 of the inflatable module 10. The restraint layer 20 is made up of high-strength fabric straps, which may be formed from a Kevlar, Vectran, or PBO narrow webbing material. More specifically, the restraint layer 20 has a woven webbing design, with both longitudinal straps 22 and hoop straps 24 orthogonal to the longitudinal straps 22. The longitudinal straps 22 and the hoop straps 24 are woven together.
Additionally, indexing stitches 26 secure the longitudinal straps 22 and hoop straps 24 together, and series of these indexing stitches form longitudinal stitch seams 27 and hoop stitch seams 28. Each indexing stitch 26 secures one hoop strap 24 to one longitudinal strap 22. Accordingly, the restraint layer 20 may be woven into a desired cylindrical, toroidal, or other inflatable module shape.
FIG. 2 also shows the rigid member 14 disposed in the restraint layer 20. Longitudinal straps 22 and hoop straps 24 intersecting the rigid member 14 are connected to a frame of the rigid member 14. The straps 22, 24 may be connected in any way known in the art. For example, connecting straps to a rigid member may include wrapping a strap around a smooth round slot or boss on the rigid member. The strap may then be woven or sewn back into the restraint layer. In one or more embodiments, a strap may be wrapped around the slot or boss and sewn back on itself to form a loop. Alternatively, the straps may be connected to the rigid member using a clevis and roller arrangement, as disclosed in Raboin.
Although including rigid members in inflatable modules is known in the art, incorporating a rigid member into an inflatable module without affecting the strength of the inflatable module is an extremely difficult engineering challenge. Because high-strength straps typically exhibit non-linear properties when stretched under load, the restraint layer of an inflatable module stretches non-linearly when an internal pressure is applied to the module (e.g., during pressurization). Furthermore, the rigid member typically exhibits a negligible amount of elongation when loaded as compared to the elongation of the restraint layer. Thus, it is difficult to analyze and predict the loads and elongation that occur in this non-linear system.